A) Field of the Invention
The present invention relates to a semiconductor device manufacture method and an etching system, and more particularly to a semiconductor device manufacture method including a process of trimming fine resist pattern such as a pattern used for patterning gate electrodes, and an etching system suitable for embodying this method.
B) Description of the Related Art
The operation speed of a MOS transistor is greatly influenced by a gate length. The shorter the gate length, the high speed operation of the transistor becomes easier. As the gate length is shortened by scaling, the gate length of 100 nm or shorter has been adopted. Such a short gate length is in excess of a photography resolution in some cases. If a gate electrode is etched by using a resist pattern itself, a gate electrode having a longer gate length than a desired size is formed.
A method of trimming a gate electrode once formed has been proposed by which after a gate electrode of polysilicon is formed, an oxide film is grown on side walls of the gate electrode through oxidation and then the oxide films are selectively etched to obtain a desired gate length (e.g., refer to Japanese Patent Laid-open Publication No. 2003-31557). With this method, a controlled oxidation process and a selective etching process are required to be added.
If the underlying layer of a resist layer including a layer to be etched has a high reflection factor such as polysilicon, a standing wave or halation may occur in the resist layer due to reflected light. In order to eliminate a standing wave and halation, a bottom anti-reflection coating (BARC) is formed under the resist layer. As BARC, an organic compound layer is widely used which has a similar composition to that of the resist layer although it has no photosensitivity.
After a BARC layer and a resist layer are formed, the resist layer is exposed and developed to form resist pattern, and then by using the resist pattern as a mask, the BARC layer is etched. If the BARC layer has a similar composition to that of the resist layer, the resist pattern is etched while the BARC layer is etched so that the size of the resist pattern is reduced.
It is said that thinning of a resist pattern can be suppressed by providing adhesion to side walls of the resist pattern by using mixed gas of oxygen gas and gas having a deposition nature such as freon. However, adhesion given to the side walls of a resist pattern is dependent upon the density of resist patterns. It is also said that there occurs a size difference between resist patterns after etching, depending upon the density of resist patterns.
A method of reducing a size difference depending on the density of resist patterns has been proposed (e.g., refer to Japanese Patent Laid-open Publication No. 2000-77386). According to this method, first main etching is executed by using mixed gas of chlorine and oxygen to minimize a conversion difference due to the pattern density, and next over etching is executed by using only halogen hydrocarbon gas, to sputter resist of the mask in an area where the patterns are dense to deposit it on side walls so that the pattern size is made thick so that a conversion difference between the resist pattern width and the anti-reflection film width is removed.
The phenomenon that a resist pattern width is reduced during patterning a BARC layer can be used for trimming a resist pattern. If a resist pattern for gate electrode patterning is to be trimmed, after a resist pattern is formed on the gate electrode layer, the width of the resist pattern is trimmed and reduced by oxygen plasma or the like, and the gate electrode layer is etched by using a narrowed resist pattern as a mask. Also in this case, the problem is the density difference between final resist pattern widths.
On the assumption that a trimming amount is dependent upon the density difference, it is possible to correct a reticle pattern for exposing resist, in order to make uniform the fine resist pattern widths. However, in the etching process, there exists a long term variation that etching products deposited on the wall of an etching system are released in a later etching process, and this long term variation changes the pattern widths due to a density difference. If this variation is to be dealt with reticle correction, the number of reticles becomes enormous, which is not practical. The pattern width of a resist layer obtained by an exposure/development process may be shifted from an expected pattern width. In this case, reticle correction provides no significant effects.